An engine control module of an internal combustion (IC) engine controls the mixture of fuel and air that is supplied to combustion chambers of the IC engine. After the spark plug ignites the air/fuel mixture, combustion gases exit the combustion chambers through exhaust valves. The combustion gases are directed by an exhaust manifold to a catalytic converter.
During certain engine operating periods, combustion gases that enter the exhaust manifold are not completely burned. The combustion gases will continue to burn in the exhaust manifold only if a sufficient amount of oxygen is available. Secondary air injection systems are typically used to inject additional air into the exhaust flow to allow combustion to continue, which reduces vehicle emissions. More particularly, prolonged combustion lowers levels of hydrocarbon (HC) and carbon monoxide (CO) emissions that are output to a catalytic converter. The additional air that is injected into the exhaust system also ensures that an adequate supply of oxygen is provided to the catalytic converter for further oxidation of HC and CO.
On-board diagnostics that are specified by government regulations require diagnostic systems that detect malfunctions in the secondary air injection systems of vehicles. Manufacturers must detect secondary air system malfunctions that cause vehicle emissions to exceed specified emission levels.